1. Field of the Invention
The present invention relates to an electrically operated valve which is used by being incorporated in a heat pump type cooling and heating system and the like, and more particularly to an electrically operated valve which can control a flow rate at a high precision at a forward flowing time (a small flow rate distributing time), and can reduce a pressure loss as much as possible at a reverse flowing time (a large flow rate distributing time).
2. Description of the Conventional Art
FIG. 6 shows an example of a heat pump type cooling and heating system. The cooling and heating system 100 is provided with a compressor 101, a flow path switching device 102, an outdoor heat exchanger (a condenser) 103, and an indoor heat exchanger (an evaporator) 104. The cooling and heating system 100 is further provided with two expansion valves (an illustration of distributors is omitted) for improving an energy saving efficiency, although one expansion valve is normally provided. In other words, a first expansion valve 105 is arranged near the outdoor heat exchanger 103, and a second expansion valve 106 is arranged near the indoor heat exchanger 104. A temperature sensing type (a mechanical type) structure is employed as the expansion valves 105 and 106. Further, in order to reduce a pressure loss as much as possible, first and second check valves 108 and 109 are arranged in parallel with the first and second expansion valves 105 and 106.
In the cooling and heating system 100, at a time of cooling, a refrigerant gas compressed by the compressor 101 is introduced to the outdoor heat exchanger 103 from the flow path switching device 102, for example, constructed by a four-way valve, as shown by a solid arrow in the drawing, and is heat exchanged here with an outside air so as to be condensed, and the condensed refrigerant flows into the second expansion valve 106 through the first check valve 108 (while bypassing the first expansion valve 105), is adiabatically expanded here, thereafter flows into the indoor heat exchanger 104, is heat exchanged with a room air by the indoor heat exchanger 104 so as to be evaporated, and cools the room.
On the contrary, at a time of heating, the refrigerant gas compressed by the compressor 101 is introduced into the indoor heat exchanger 104 from the flow path switching device 102 as shown by a broken arrow in the drawing, is heat exchanged here with the room air so as to be condensed, heats the room, thereafter passes through the second check valve 109 (while bypassing the second expansion valve 106), flows into the first expansion valve 105, is depressurized here, is thereafter introduced to the outdoor heat exchanger 103 via the distributor, is evaporated here, and is returned to the compressor 101.
As mentioned above, in the cooling and heating system 100, at a time of the forward flowing (at a time of cooling), the refrigerant is introduced to the second expansion valve 106 through the first check valve 108 without passing through the first expansion valve 105, and the flow rate is regulated by the second expansion valve 106, and at a time of the backward flowing (at a time of heating), the refrigerant is introduced to the first expansion valve 105 through the second check valve 109 without passing through the second expansion valve 106, and the flow rate is regulated by the first expansion valve 105. Accordingly, the pressure loss can be reduced as much as possible by incorporating the check valves 108 and 109 in parallel with the expansion valves 105 and 106.
In the meantime, in recent years, in the cooling and heating system 100 as mentioned above, there has been considered to employ an electronically controlled type electrically operated valve which can optionally control a lift amount, that is, an effective opening area of a valve port, in place of the temperature sensing type (the mechanical type) expansion valves 105 and 106, for further improving the energy saving efficiency.
A description will be given below of an example of the electronically controlled type electrically operated valve with reference to FIG. 7. An electrically operated valve 10′ in an illustrated example is provided with a valve shaft 25 which has a lower large-diameter portion 25a and an upper small-diameter portion 25b, and is integrally provided with a valve body 24 in a lower end portion of the lower large-diameter portion 25a, a valve main body 15 which is provided with a valve seat 23A forming a valve port 23 which the valve body 24 comes into contact with and away from, and has a valve chamber 21 to which a first inlet and outlet 11 and a second inlet and outlet 12 constructed by a conduit (a joint) are connected, a can 40 which is hermetically joined its lower end portion to the valve main body 15 via an annular coupling device 44 by welding, a rotor 30 which is arranged in an inner periphery of the can 40 so as to be spaced at a predetermined distance α, a stator 50A which is outward fitted to the can 40 so as to rotationally drive the rotor 30, and a screw feed mechanism which is arranged between the rotor 30 and the valve body 24, and brings the valve body 24 into contact with and away from the valve port 23 by utilizing a rotation of the rotor 30, and is structured such as to control a passing flow rate of the refrigerant by changing a lift amount of the valve body 24 in relation to the valve port 23.
The stator 50A is constructed by a yoke 51, a bobbin 52, stator coils 53 and 53, and a resin mold cover 56, a stepping motor 50 is constructed by the rotor 30 and the stator 50A, and an elevation drive mechanism for regulating a lift amount of the valve body 24 in relation to the valve port 23 is constructed by the stepping motor 50 and the screw feed mechanism (mentioned later).
A support ring 36 is integrally coupled to the rotor 30, and an upper protruding portion of a tubular valve shaft holder 32 is fixed by caulking to the support ring 36, the valve shaft holder 32 being arranged in an outer periphery of the valve shaft 25 and a guide bush 26 and being open downward. Accordingly, the rotor 30, the support ring 36 and the valve shaft holder 32 are integrally coupled.
The screw feed mechanism is constructed by a fixed thread portion (a male thread portion) 28 which is formed in an outer periphery of the tubular guide bush 26, the tubular guide bush 26 being structured such that a lower end portion 26a is pressure fixed to the valve main body 15, and (the lower large-diameter portion 25a of) the valve shaft 25 is inward inserted to the guide bush 26 slidably, and a movable thread portion (a female thread portion) 38 which is formed in an inner periphery of the valve shaft holder 32 and is threadably engaged with the fixed thread portion 28.
Further, an upper small-diameter portion 26b of the guide bush 26 is inward inserted to an upper portion of the valve shaft holder 32, and the upper small-diameter portion 25b of the valve shaft 25 is inserted to (a through hole formed in) a center of a ceiling portion 32a of the valve shaft holder 32. A push nut 33 is pressure fixed to an upper end portion of the upper small-diameter portion 25b of the valve shaft 25.
Further, the valve shaft 25 is normally energized downward (in a valve closing direction) by a valve closing spring 34 constructed by a compression spring which is outward inserted to the upper small-diameter portion 25b of the valve shaft 25, and is provided in a compressed manner between the ceiling portion 32a of the valve shaft holder 32 and an upper end terrace surface of the lower large-diameter portion 25a in the valve shaft 25. A return spring 35 constructed by a coil spring is provided in an outer periphery of the push nut 33 on the ceiling portion 32a of the valve shaft holder 32.
A lower stopper body (a fixed stopper) 27 is firmly fixed to the guide bush 26, the lower stopper body 27 constructing one of a rotation downward movement stopper mechanism for inhibiting a further rotation and downward movement in the case that the rotor 30 is rotated and downward moved to a predetermined valve closing position, and an upper stopper body (a movable stopper) 37 is firmly fixed to the valve shaft holder 32, the upper stopper body 37 constructing the other of the stopper mechanism.
The valve closing spring 34 is provided for obtaining a desired sealing pressure (preventing leakage) in a valve closing state in which the valve body 24 seats on the valve port 23, and buffering a shock at a time when the valve body 24 comes into collision with the valve port 23.
In the electrically operated valve 10′ structured as mentioned above, the rotor 30 and the valve shaft holder 32 are rotated in one direction in relation to the guide bush 26 which is fixed to the valve body 15, by feeding a conduction exciting pulse to the stator coils 53 and 53 according to a first mode, and the valve body 24 is pressed against the valve port 23 (the valve seat 23A), for example, on the basis of a downward movement of the valve shaft holder 32, by screw feeding the fixed screw portion 28 of the guide bush 26 and the movable thread portion 38 of the valve shaft holder 32, whereby the valve port 23 is closed (a full close state).
At a time point that the valve port 23 is closed, the upper stopper body 37 does not come into collision with the lower stopper body 27 yet, and the rotor 30 and the valve shaft holder 32 further rotate and move downward in a state in which the valve body 24 closes the valve port 23. In this case, since the valve shaft 25 (the valve body 24) does not move downward, however, the valve shaft holder 32 moves downward, the valve closing spring 34 is compressed at a predetermined amount. As a result, the valve body 24 is strongly pressed to the valve port 23, and the upper stopper body 37 comes into collision with the lower stopper body 27 on the basis of the rotation and the downward movement of the valve shaft holder 32. Accordingly, even if the pulse feed to the stator coils 53 and 53 is carried on thereafter, the rotation and the downward movement of the valve shaft holder 32 are forcibly stopped.
On the other hand, if the conduction exciting pulse is fed to the stator coils 53 and 53 according to a second mode, the rotor 30 and the valve shaft holder 32 are rotated in the inverse direction to the above in relation to the guide bush 26 which is fixed to the valve main body 15, and the valve shaft holder 32 moves upward at this time on the basis of the screw feed of the fixed thread portion 28 of the guide bush 26 and the movable thread portion 38 of the valve shaft holder 32. In this case, since the valve closing spring 34 is compressed at a predetermined amount as mentioned above at a time point that the valve shaft holder 32 starts rotating and moving upward (a time point that the pulse feed is started), the valve body 24 is not disconnected and keeps the valve closing state (lift amount=0), until the valve closing spring 34 elongates at the predetermined amount. Further, if the valve shaft holder 32 is further rotated and moved upward after the valve closing spring 34 elongates at the predetermined amount, the valve body 24 is disconnected from the valve port 23, the valve port 23 is opened, and the refrigerant passes through the valve port 23. In this case, it is possible to optionally and finely regulate the lift amount of the valve body 24, that is, the effective opening area of the valve port 23 on the basis of an amount of rotation of the rotor 30. Since the amount of rotation of the rotor 30 is controlled by a feed pulse number, it is possible to precisely control the flow rate of the refrigerant (refer the details to Japanese Unexamined Patent Publications No. 2001-50415 and No. 2009-14056).
Even in the case that the electrically operated valve 10′ as mentioned above is employed in the cooling and heating system 100, there is the following problem to be improved. In other words, in the cooling and heating system 100, since the refrigerant is conducted to the second expansion valve 106 through the first check valve 108 without passing through the first expansion valve 105 and the flow rate is regulated by the second expansion valve 106, at the forward flowing time (the cooling time), and the refrigerant is conducted to the first expansion valve 105 through the second check valve 109 without passing through the second expansion valve 106, and the flow rate is regulated by the first expansion valve 105, at the inversely flowing time (the heating time), it is indispensable to incorporate the check valves 108 and 109 in parallel with the expansion valves 105 and 106. However, in the case that two check valves are incorporated in the refrigerant circuit, the number of the parts such as the joints is increased at that degree, and it takes a lot of labor and long time unnecessarily to carry out a piping connecting work. Accordingly, in Japanese Unexamined Patent Publication No. 2009-14056, there has been proposed an electrically operated valve having both the functions of the expansion valve and the check valve, that is, the electrically operated valve structured such that a lift amount (an effective opening area) is finely controlled in a specific range which is equal to or less than a predetermined value, for carrying out a flow rate control, at a time when the refrigerant is flowed in one direction (a forward flowing time=a small flow rate distributing time), and the lift amount (the effective opening area) is set to the maximum for reducing the pressure loss as much as possible, at a time when the refrigerant is flowed in the other direction (an inversely flowing time=a large flow rate distributing time).
However, in the electrically operated valve proposed above, in the case that a bore diameter of a valve port is enlarged for reducing the pressure loss at the large flow rate distributing time, there is a problem that it is impossible to carry out the flow rate control at a high precision at the small flow rate distributing time.
On the other hand, in order to achieve both the reduction of the pressure loss at the large flow rate distributing time and the improvement of the flow rate control precision at the small flow rate distributing time, there has been proposed a bidirectional distribution type electrically operated valve having a valve main body which is provided with a first inlet and outlet, a valve chamber, a lower chamber and a second inlet and outlet, a movable valve seat body which is arranged within the valve chamber, forms a main valve port for forming a small flow rate flow path extending from the first inlet and outlet to the second inlet and outlet, and serving also as a float type check valve body for opening and blocking a large flow rate flow path extending from the second inlet and outlet to the first inlet and outlet, a valve shaft which has a needle type valve body portion arranged within the valve chamber for regulating a flow rate passing through the main valve port, and a motor for moving up and down the valve shaft, and structured such as to close the large flow rate flow path by the movable valve seat body so as to circulate a fluid only a portion between the valve body portion and the main valve port for precisely carrying out a flow rate control at a small flow rate distributing time, and open the large flow rate flow path by making the movable valve seat body (the check valve body) float for reducing the pressure loss as much as possible at a large flow rate distributing time, as described in Japanese Unexamined Patent Publication No. 2009-287913.